Tamper-resisting screw-threaded plug

ABSTRACT

A tamper-resisting screw-threaded plug includes a cylindrical main body with a screw-threaded outer side wall. The body has an annular recess in the front face which is bounded on its radially outer side by a peripheral wall of the main boyd and on its radially inner side by a central hub of the main body. The hub is shaped for engagement by a correct tool of predetermined shape to enable the plug to be rotated by the tool. The plug also includes a sleeve secured in the recess adjacent the peripheral wall of the main body so as to be rotatable relative thereto, the sleeve being radially spaced from the central hub to enable the tool to be engaged therewith. The sleeve has an outwardly directed annular flange extending over a front face of the peripheral wall of the main body to prevent engagement of the front face by an incorrect tool.

[ Oct. 14, 1975 [54] TAMPER-RESISTING SCREW-THREADED PLUG [75] Inventor:William Chahley, Saint John,

'Canada [73] Assignee: Wm. Chahley Ltd., Saint John,

Canada 22 Filed: Aug. 23, 1974 21 Appl. No.: 499,943

[30] Foreign Application Priority Data Mar. 27, 1974 Canada 196136 [52]US. Cl 220/288; 220/284 [51] Int. Cl. B65D 41/04 [58] Field of Search220/284, 288, 298, 301, 220/304, 307; 138/96 R, 89

[56] References Cited UNITED STATES PATENTS 1,422,342 7/1922 Darling220/284 1,712,361 5/1929 Soderquist. 220/284 2,663,451 12/1953 Yarnall220/284 2,801,022 7/1957 Evenb1is.. 220/288 3,195,762 7/1965 Senoff220/284 3,380,618 4/1968 vPhillips 220/284 Primary ExaminerWilliam 1.Price Assistant ExaminerR. E. Hart Attorney, Agent, or FirmBrowne,Beveridge, DeGrandi & Kline [57] ABSTRACT A tamper-resistingscrew-threaded plug includes a cylindrical main body with ascrew-threaded outer side wall. The body has an annular recess in thefront face which is bounded on its radially outer side by a peripheralwall of the main boyd and on its radially inner side by a central hub ofthe main body. The hub is shaped for engagement by a correct tool ofpredetermined shape to enable the plug to be rotated by the tool. Theplug also includes a sleeve secured in the recess adjacent theperipheral wall of the main body so as to be rotatable relative thereto,the sleeve being radially spaced from the central hub to enable the toolto be engaged therewith. The sleeve has an outwardly directed annularflange extending over a front face of the peripheral wall of the mainbody to prevent engagement of the front face by an incorrect tool.

6 Claims, 5 Drawing Figures Oct. 14, 1975 US. Patent TAMPER-RESISTINGSCREW-THREADED PLUG This invention relates to tamper-resistingscrewthreaded plugs, that is to say. plugs which are constructed toresist'removal by unauthorized persons.

There are many situations where such plugsa're required to be resistantto removal by unauthorized persons, but nevertheless capable of removalby authorized persons. Such a plug can be constructed so that it isremovable by an authorized person with a specially shaped correct tool,but is resistant to removal by an unauthorized person with a tool, suchas a common tool, of some other shape. I

It is therefore an object of the invention: to provide an improved plugof this kind. I

According to the invention, a plug includes a cylindrical main body witha'screw-threaded outer side wall, the body having an annular recess inits front face, the annular recess being bounded on its radially outerside by a peripheral wall and on its radially inner side by a centralhub, the hub being shaped for engagement by a correct tool ofpredetermined shape to enable the plug to be rotated by the tool, theplug also including a sleeve secured in the recess adjacent theperipheral wall of the body so as to be rotatable relative to the body,the sleeve being spaced from the central hub to enable the tool to beengaged therewith, and the sleeve having an outwardly directed annularflange extending over the front face of the peripheral wall of the body.

Thus, the plug cannot be rotated for removal from a screw-threadedaperture by a tool engaging the peripheral wall of the body, since theperipheral wall is protected by the sleeve and its flange. Rotation ofthe sleeve and its flange by a tool does not rotate the main body of thenut. The main body of the nut can only by rotated by a tool engaging thecentral hub.

The hub may be cylindrical, so as to resist rotation by tools such aspliers, and may have a plurality of longitudinally extending grooves forengagement by an appropriately shaped correct removal tool. The forwardends of the grooves may be laterally flared, so as to form a further barto engagement by tools other than the correct tool. Also, the peripheryof the hub may be chamfered as a further bar to unauthorized removal.

The body recess may contain a retaining ring tightly engaging theperipheral wall and spaced from the bot tom of the recess, the sleevehaving a groove in its outer surface, the groove containing a springclip engaging the rear end of the retaining ring to retain the sleeve inthe recess, while allowing relative rotation between the sleeve and themain body.

The sleeve may also have an inwardly directed annular flange within therecess, adjacent the bottom thereof, so as to prevent engagement of thebottom of the recess by a tool. 7

One embodiment of the invention will now be described, by way ofexample, with reference to the accompanying drawings, of which:

FIG. 1 is a sectional side view of a plug,

FIG. 2 is a front view of a plug,

FIG. 3 is a side view of a correct too] for use with the P g FIG. 4 is afront view of the tool, and

FIG. 5 is a sectional side view showing the tool engaged with the plug.

Referring to the drawings, the plug has a cylindrical main body 11 witha screw-threaded outer side wall 12.

The body 11 has an annular recess 13 in its front face 14, recess 13being bounded on its radially outer side by a peripheral wall 15 and onits radially inner side by a central hub 16.

The recess 13 contains a retaining ring 17 which is a press fit withtheperipheral wall 15, so as to be fixed thereto. The front end of thering 17 is flush with the front face l4 of the body ll, and the rear endof the ring 17 is spaced from the bottom of the recess 13. A sleeve 18is located. in the recess 13, and is a loose fit in the retaining ringso as to be rotatable relative thereto. sleeve 18 extends for the wholedepth of the recess 13. The sleeve 18 has an annular groove in its outerwall which contains a spring clip 19. The clip 19 projects from thegroove and is engaged behind the rear end of the retaining ring 17, sothat the retaining ring 17 retains the sleeve 18 in the recess 13, whileallowing the sleeve 18 to be-capable of rotation relative to theretaining ring 17 and the main body 1 1 of the plug.

The sleeve 18 has a radially outwardly directed annular flange 21 at itsfront end extending across the front face of the peripheral wall 15, andalso has a radially inwardly directed annular flange 22 at its rear endextending across the bottom of the recess 13. Two drain holes 23 extendfrom the bottom of the recess 13 to the rear face of the plug.

The hub 16 is cylindrical, and has three equiangularly spacedlongitudinally extending grooves 24, which extend for the full length ofthe hub 16. The front end of each groove 24 is flared laterallyoutwardly at 25, and the periphery of the hub 16 is chamfered at 20.

A correct tool for use with the plug has a tubular body 26 with threeradially-inwardly extending fingers 27 at one end. The fingers 27 arepositioned and shaped for engagement in the grooves 24 of the hub 16. Toinsert the plug in, or remove it from, a screwthreaded aperture ofappropriate size, the tool fingers 27 are slid into the hub grooves 24.The tool is then rotated by any suitable other instrument.

To rotate the plug, it is necessary to have the correct tool. Commontools cannot easily be used to turn the plug. For example, the outersleeve flange 21 protects the front face of the peripheral wall of themain body 1 1 from any screwdriver or chisel hammer blows, which may beapplied in an attempt to rotate the plug or create indentations forfuture rotation attempts. The sleeve flange 21 will merely rotaterelative to the body 1 1 under such blows. The inner flange 22 similarlyprotects the bottom of the recess 13.

Also, the hub 16 cannot be effectively grasped by such tools as pliersor vice grips, particularly in view of the chamfer 20. If any chisel orscrewdriver attempt is made to turn the hub 16, the flaring 25facilitates shearing of the front end portion of the hub 16, therebyrendering such attempts ineffective. In any event, the hub 16 is of toosmall a diameter to enable any effective turning movement to be appliedthereto by a chisel or screwdriver.

It will be seen that the described plug is extremely resistant tounauthorized removal. The described plug is actually intended for use asthe closing plug in the manhole cover which is the subject of CanadianPat. No. 937,089, issued Nov. 20, 1973, but of course the invention isnot limited to such use.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A tamper-resisting screw-threaded plug including a cylindrical mainbody with a screw-threaded outer side wall, the body having an annularrecess in the front face thereof, the annular recess being bounded onits radially outer side by a peripheral wall of the main body and on itsradially inner side by a central hub of the main body, the hub beingshaped for engagement by a correct tool of predetermined shape to enablethe plug to be rotated by the tool, the plug also including a sleevesecured in the recess adjacent the peripheral wall of the main body soas to be rotatable relative thereto, the sleeve being radially spacedfrom the central hub to enable the tool to be engaged therewith, thesleeve having an outwardly directed annular flange extending over afront face of the peripheral wall of the main body to prevent engagementof said front face by an incorrect tool.

2. A plug according to claim 1 wherein the hub is cylindrical and has aplurality of longitudinally extending grooves for engagement by thecorrect tool.

3. A plug according to claim 2 wherein the grooves have forward endswhich are laterally flared.

4. A plug according to claim 1 wherein the periphery of the hub ischamfered.

5. A plug according to claim 1 wherein the sleeve also has an inwardlydirected annular flange within the recess and adjacent the bottomthereof.

6. A plug according to claim 1 including a retaining ring within therecess and tightly engaging the peripheral wall, the retaining ringbeing spaced from the bottom of the recess, the sleeve having a groovein its outer surface, and the groove containing a spring clip engaging arear end of the retaining ring to secure the sleeve in the recess, whileallowing relative rotation between the sleeve and the main body.

1. A tamper-resisting screw-threaded plug including a cylindrical mainbody with a screw-threaded outer side wall, the body having an annularrecess in the front face thereof, the annular recess being bounded onits radially outer side by a peripheral wall of the main body and on itsradially inner side by a central hub of the main body, the hub beingshaped for engagement by a correct tool of predetermined shape to enablethe plug to be rotated by the tool, the plug also including a sleevesecured in the recess adjacent the peripheral wall of the main body soas to be rotatable relative thereto, the sleeve being radially spacedfrom the central hub to enable the tool to be engaged therewith, thesleeve having an outwardly directed annular flange extending over afront face of the peripheral wall of the main body to prevent engagementof said front face by an incorrect tool.
 2. A plug according to claim 1wherein the hub is cylindrical and has a plurality of longitudinallyextending grooves for engagement by the correct tool.
 3. A plugaccording to claim 2 wherein the grooves have forward ends which arelaterally flared.
 4. A plug according to claim 1 wherein the peripheryof the hub is chamfered.
 5. A plug according to claim 1 wherein thesleeve also has an inwardly directed annular flange within the recessand adjacent the bottom thereof.
 6. A plug according to claim 1including a retaining ring within the recess and tightly engaging theperipheral wall, the retaining ring being spaced from the bottom of therecess, the sleeve having a groove in its outer surface, and the groovecontaining a spring clip engaging a rear end of the retaining ring tosecure the sleeve in the recess, while allowing relative rotationbetween the sleeve and the main body.